WAFER PROCESSING METHOD
A wafer processing method including a wafer supporting step of attaching a front side of a dicing tape formed of synthetic resin to a back side of a wafer and supporting a peripheral portion of the dicing tape to an annular frame, a dicing tape heating step of heating a back side of the dicing tape attached to the wafer to soften the dicing tape, thereby flattening the back side of the dicing tape, and a modified layer forming step of applying a laser beam having a transmission wavelength to the wafer through the dicing tape from the back side thereof along the division lines in the condition where the focal point of the laser beam is set inside the wafer, thereby forming a modified layer inside the wafer along each division line.
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1. Field of the Invention
The present invention relates to a wafer processing method of dividing a wafer into a plurality of devices along a plurality of division lines, the devices being formed on a front side of the wafer and partitioned by the division lines.
2. Description of the Related Art
As well known in the art, in a semiconductor device fabrication process, a functional layer composed of an insulating film and a functional film is formed on a front side of a substrate such as a silicon substrate, and a plurality of semiconductor devices such as ICs and LSIs are formed like a matrix from this functional layer, thus obtaining a semiconductor wafer having the plural semiconductor devices. The plural semiconductor devices are partitioned by a plurality of crossing division lines formed on a front side of the semiconductor wafer. The semiconductor wafer is divided along these division lines to obtain the individual semiconductor devices as chips.
Further, in an optical device fabrication process, an optical device wafer is provided by forming an optical device layer composed of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a front side of a sapphire substrate or a silicon carbide substrate. The optical device layer is partitioned by a plurality of crossing division lines to define a plurality of regions where a plurality of optical devices such as light emitting diodes and laser diodes are respectively formed. The optical device wafer is cut along the division lines to thereby divide the regions where the optical devices are formed from each other, thus obtaining the individual optical devices as chips.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the division lines, there has been tried a laser processing method of applying a pulsed laser beam having a transmission wavelength to the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the wafer in a subject area to be divided. More specifically, this wafer dividing method using laser processing includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side of the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the wafer to thereby continuously form a modified layer inside the wafer along each division line and next applying an external force to the wafer along each division line where the modified layer is formed to be reduced in strength, thereby dividing the wafer into the individual devices (see Japanese Patent No. 3408805, for example).
In the above method of forming a modified layer inside the wafer along each division line and dividing the wafer along each division line where the modified layer is formed, the modified layer is formed inside the wafer in which the width of each division line is small. Accordingly, it is desirable to apply the laser beam to the wafer from the back side thereof where the devices are not formed. Further, in a pickup step of picking up each device after dividing the wafer along each division line, it is desirable to expose the front side of the wafer where the devices are formed. For these reasons, the wafer is divided in the following manner. First, a laser beam having a transmission wavelength to the wafer is applied to the wafer from the back side thereof along each division line to thereby form a modified layer inside the wafer along each division line. Thereafter, a dicing tape is attached to a back side of the wafer, and a peripheral portion of the dicing tape is supported to an annular frame. Thereafter, an external force is applied to the wafer to thereby divide the wafer into the individual devices (see Japanese Patent Laid-open No. 2006-54246, for example).
However, in the case that the dicing tape is attached to the back side of the wafer after forming the modified layer inside the wafer along each division line, there is a possibility that the wafer may be broken. To cope with this problem, there has been proposed a method such that a front side of a dicing tape is attached to the back side of a wafer and the peripheral portion of the dicing tape is supported to an annular frame prior to forming a modified layer inside the wafer along each division line. Thereafter, a laser beam having a transmission wavelength to the wafer is applied to the wafer through the dicing tape from the back side thereof along each division line in the condition where the focal point of the laser beam is set inside the wafer, thereby forming the modified layer inside the wafer along each division line (see Japanese Patent Laid-open No. 2012-84618, for example).
However, a back side of the dicing tape has fine asperities, causing a problem such that the transmission of the laser beam is hindered and the laser beam cannot be sufficiently focused inside the wafer, so that a desired modified layer cannot be formed. To solve this problem, the technique described in Japanese Patent Laid-open No. 2012-84618 includes a flattening step of applying a liquid resin to the back side of the dicing tape to thereby flatten the back side of the dicing tape. After performing the flattening step, the laser beam having a transmission wavelength to the wafer is applied to the wafer through the dicing tape from the back side thereof along each division line in the condition where the focal point of the laser beam is set inside the wafer, thereby forming the modified layer.
SUMMARY OF THE INVENTIONIn the technique described in Japanese Patent Laid-open No. 2012-84618 mentioned above, the liquid resin is applied to the back side of the dicing tape in order to flatten the back side of the dicing tape. However, it is difficult to form the layer of the liquid resin into a flat surface. Further, a laser processing apparatus for forming the modified layer must be equipped with a resin applying apparatus for applying the liquid resin.
It is therefore an object of the present invention to provide a wafer processing method which can easily flatten the back side of the dicing tape and can form a desired modified layer inside the wafer along each division line by applying a laser beam having a transmission wavelength to the wafer through the dicing tape from the back side thereof along each division line in the condition where the focal point of the laser beam is set inside the wafer.
In accordance with an aspect of the present invention, there is provided a wafer processing method of dividing a wafer into a plurality of devices along a plurality of division lines, the devices being formed on the front side of the wafer and partitioned by the division lines, the wafer processing method including a wafer supporting step of attaching the front side of a dicing tape formed of synthetic resin to the back side of the wafer and supporting the peripheral portion of the dicing tape to an annular frame; a dicing tape heating step of heating the back side of the dicing tape attached to the wafer to soften the dicing tape after performing the wafer supporting step, thereby flattening the back side of the dicing tape; and a modified layer forming step of applying a laser beam having a transmission wavelength to the wafer through the dicing tape from the back side thereof along the division lines in the condition where the focal point of the laser beam is set inside the wafer after performing the dicing tape heating step, thereby forming a modified layer inside the wafer along each division line.
Preferably, the dicing tape heating step includes the step of using hot air having a temperature of 100° C. or more to heat the back side of the dicing tape. Preferably, the wafer processing method further includes a wafer dividing step of applying an external force to the wafer after performing the modified layer forming step, thereby dividing the wafer into the individual devices along the division lines where the modified layers are respectively formed.
In the wafer processing method according to the present invention, the wafer supporting step is first performed to attach the front side of the dicing tape formed of synthetic resin to the back side of the wafer, and the peripheral portion of the dicing tape is supported to the annular frame. After performing the wafer supporting step, the dicing tape heating step is performed to heat the back side of the dicing tape attached to the wafer to soften the dicing tape, thereby flattening the back side of the dicing tape. After performing the dicing tape heating step, the modified layer forming step is performed to apply a laser beam having a transmission wavelength to the wafer through the dicing tape from the back side thereof along the division lines in the condition where the focal point of the laser beam is set inside the wafer, thereby forming a modified layer inside the wafer along each division line. Therefore, the back side of the dicing tape is flattened prior to performing the modified layer forming step. Accordingly, the laser beam can be reliably focused at a predetermined position inside the wafer, so that a desired modified layer can be formed inside the wafer along each division line.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.
A wafer processing method according to the present invention will now be described in more detail with reference to the attached drawings.
To divide the semiconductor wafer 2 along the division lines 21, a wafer supporting step is first performed in such a manner that the front side of a dicing tape formed of synthetic resin is attached to the back side 2b of the semiconductor wafer 2 and the peripheral portion of the dicing tape is supported to an annular frame. More specifically, as shown in
After performing the wafer supporting step mentioned above, a dicing tape heating step is performed in such a manner that the back side 30b of the dicing tape 30 attached to the semiconductor wafer 2 is heated to soften the dicing tape 30 and thereby flatten the back side 30b of the dicing tape 30. As shown in
After performing the dicing tape heating step mentioned above, a modified layer forming step is performed in such a manner that a laser beam having a transmission wavelength to the semiconductor wafer 2 is applied through the dicing tape 30 from the back side 30b thereof along the division lines 21 in the condition where the focal point of the laser beam is set inside the semiconductor wafer 2, thereby forming a modified layer inside the semiconductor wafer 2 along each division line 21. This modified layer forming step is performed by using a laser processing apparatus 5 shown in
The laser beam applying means 52 includes a cylindrical casing 521 extending in a substantially horizontal direction. Although not shown, the casing 521 contains pulsed laser beam oscillating means including a pulsed laser beam oscillator and repetition frequency setting means. The laser beam applying means 52 further includes focusing means 522 mounted on the front end of the casing 521 for focusing a pulsed laser beam oscillated by the pulsed laser beam oscillating means. The laser beam applying means 52 further includes focal position adjusting means (not shown) for adjusting the focal position of the pulsed laser beam to be focused by the focusing means 522.
The imaging means 53 is mounted on a front end portion of the casing 521 constituting the laser beam applying means 52. The imaging means 53 includes an ordinary imaging device (CCD) for imaging the workpiece by using visible light, infrared light applying means for applying infrared light to the workpiece, an optical system for capturing the infrared light applied to the workpiece by the infrared light applying means, and an imaging device (infrared light CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system. An image signal output from the imaging means 53 is transmitted to control means (not shown).
The modified layer forming step using the laser processing apparatus 5 will now be described with reference to
First, the semiconductor wafer 2 attached to the dicing tape 30 is placed on the chuck table 51 of the laser processing apparatus 5 shown in
In the condition where the chuck table 51 is positioned directly below the imaging means 53, an alignment operation is performed by the imaging means 53 and the control means (not shown) to detect a subject area of the semiconductor wafer 2 to be laser-processed. More specifically, the imaging means 53 and the control means perform image processing such as pattern matching for making the alignment of the division lines 21 extending in a first direction on the semiconductor wafer 2 and the focusing means 522 of the laser beam applying means 52 for applying the laser beam to the wafer 2 along the division lines 21, thus performing the alignment of a laser beam applying position (alignment step). Similarly, this alignment step is performed for the other division lines 21 extending in a second direction perpendicular to the first direction on the semiconductor wafer 2. Although the front side 2a of the semiconductor wafer 2 on which the division lines 21 are formed is oriented downward, the division lines 21 can be imaged through the dicing tape 30 and the semiconductor wafer 2 from the back side 2b thereof because the imaging means 53 includes the infrared light applying means for applying infrared light to the wafer 2, the optical system for capturing the infrared light applied to the wafer 2, and the imaging device (infrared light CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system as described above.
After performing the alignment step mentioned above for all of the division lines 21, the chuck table 51 is moved to a laser beam applying area where the focusing means 522 of the laser beam applying means 52 is located as shown in
For example, the modified layer forming step mentioned above is performed under the following processing conditions.
Light source: YAG pulsed laser
Wavelength: 1064 nm
Repetition frequency: 80 kHz
Average power: 0.2 W
Work feed speed: 180 mm/s
After performing the modified layer forming step along the predetermined division line 21 as mentioned above, the chuck table 51 is moved in the indexing direction shown by the arrow Y in
As described above, the laser beam having a transmission wavelength to the wafer is applied through the dicing tape 30 from the back side 30b thereof along the division lines 21 in the condition where the focal point of the laser beam is set inside the semiconductor wafer 2 in the modified layer forming step. In the dicing tape heating step to be performed prior to the modified layer forming step, the back side 30b of the dicing tape 30 is flattened. Accordingly, the laser beam can be reliably focused at a predetermined position inside the semiconductor wafer 2, so that the desired modified layer 23 can be formed inside the semiconductor wafer 2 along each division line 21.
After performing the modified layer forming step mentioned above, a wafer dividing step is performed in such a manner that an external force is applied to the semiconductor wafer 2 to divide the semiconductor wafer 2 along the division lines 21 where the modified layers 23 are respectively formed, thereby obtaining the individual devices 22. This wafer dividing step is performed by using a dividing apparatus 6 shown in
The tape expanding means 62 includes an expanding drum 621 provided inside of the annular frame holding member 611. The expanding drum 621 has an outer diameter smaller than the inner diameter of the annular frame 3 and an inner diameter larger than the outer diameter of the semiconductor wafer 2 attached to the dicing tape 30 supported to the annular frame 3. The expanding drum 621 has a supporting flange 622 at the lower end of the expanding drum 621. The tape expanding means 62 further includes supporting means 623 for vertically movably supporting the annular frame holding member 611. The supporting means 623 is composed of a plurality of air cylinders 623a provided on the supporting flange 622. Each air cylinder 623a is provided with a piston rod 623b connected to the lower surface of the annular frame holding member 611. The supporting means 623 composed of these plural air cylinders 623a functions to vertically move the annular frame holding member 611 so as to selectively take a reference position where the mounting surface 611a is substantially equal in height to the upper end of the expanding drum 621 as shown in
The wafer dividing step using the dividing apparatus 6 will now be described with reference to
Thereafter, the pickup collet 63 is operated to hold each device 22 under suction and peel it from the dicing tape 30, thereby individually picking up the devices 22 as shown in
The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
Claims
1. A wafer processing method of dividing a wafer into a plurality of devices along a plurality of division lines, said devices being formed on a front side of said wafer and partitioned by said division lines, said wafer processing method comprising:
- a wafer supporting step of attaching a front side of a dicing tape formed of synthetic resin to a back side of said wafer and supporting a peripheral portion of said dicing tape to an annular frame;
- a dicing tape heating step of heating a back side of said dicing tape attached to said wafer to soften said dicing tape after performing said wafer supporting step, thereby flattening the back side of said dicing tape; and
- a modified layer forming step of applying a laser beam having a transmission wavelength to said wafer through said dicing tape from the back side thereof along said division lines in a condition where the focal point of said laser beam is set inside said wafer after performing said dicing tape heating step, thereby forming a modified layer inside said wafer along each division line.
2. The wafer processing method according to claim 1, wherein said dicing tape heating step comprises the step of using hot air having a temperature of 100° C. or more to heat the back side of said dicing tape.
3. The wafer processing method according to claim 1, further comprising
- a wafer dividing step of applying an external force to said wafer after performing said modified layer forming step, thereby dividing said wafer into said individual devices along said division lines where said modified layers are respectively formed.
Type: Application
Filed: Apr 21, 2014
Publication Date: Oct 23, 2014
Patent Grant number: 9379016
Applicant: DISCO CORPORATION (Tokyo)
Inventor: Masaru Nakamura (Tokyo)
Application Number: 14/257,601
International Classification: H01L 21/78 (20060101);